THE PHASE-DIAGRAM AND CRYSTAL-GROWTH OF (Y1-XPRX)BA2CU3O7-Y

Y1-xPrxBa2Cu3O7-y is a unique superconductive material for the investigation of the interrelation between crystal structure, chemical composition and physical properties. In order to grow large crystals of high quality, an extensive study has been made of the Y2O3-Pr6O11-BaO-CuO growth system. The eutectic composition of the BaO-CuO flux is confirmed by the improved thermogravimetric method (ITGA) as occurring at the molar composition of 7:18. The pseudo-binary phase diagram of (Y, Pr)BCO-(7BaO + 18CuO) has been determined by means of differential thermal analysis (DTA), by X-ray diffraction and by study of crystal growth. Using the phase diagram, suitable compositions and temperature programs have been established for the growth of large crystals and for the separation of the crystals from the flux. Single crystals with a wide range of Pr doping have been obtained from a eutectic BaO-CuO flux. The dependence of the Pr concentration in the crystals on the composition of the initial melt has been determined by electron probe microanalysis and X-ray microanalysis. The superconducting transition temperature is found to decrease monotonically with increasing Pr concentration.